One of the main themes of the movie is that people do not see what is directly in front...

One of the main themes of the movie is that people do not see what is directly in front of them because they're too self involved or they are too conditioned by stereotypes. How is this theme illustrated in Arsenic and Old Lace?

O'Hara is a policeman who sees a crime being committed right before his eyes and yet he has no clue. Even though Mortimer, bound and gagged, tries to send him nonverbal clues, O'Hara sees nothing odd about the situation. He buys Dr. Einstein's explanation of these circumstances when Einstein tells the policeman that Mortimer is acting out a scene from a play. Mortimer, who critiques plays, is a "captive" audience while O'Hara shares his ideas for a play he is writing. The policeman is blinded to the reality of the situation because he is so interested in a career as a playwright that he loses sight of his responsibility as a policeman.

The other policemen support the theme as they run around like Keystone cops. Phone calls are being made and Uncle Teddy is blowing his bugle upstairs. The police are chattering about O'Hara not checking in, the need to contact the station, and the complaints by the neighbors over the bugle blowing. Each policeman is so caught up with his own concerns that all lose sight of playing as a team to catch the bad guy. Though alerts have been sent out about Jonathan, and the officers even discuss it, not one takes a hard look at the situation developing until it's almost too late.

The sergeant carries on conversations with O'Hara and other police on the scene, even describing the two fugitives in the room with him: the murderer who looks like Boris Karloff and and his accomplice--a little man posing as a doctor. When Mortimer gets free, he even calls Dr. Einstein by name, but by this time the police have bigger problems.

The police nearly let Jonathan escape, but Jonathan actually draws attention to his identity doing the police's work for them. When he starts to confess to his crimes, the police finally realize they have the Boris-Karloff-look-alike murderer beneath their noses. Once again, keeping all their attention on subduing Jonathan, they allow Dr. Einstein to slip away.